Oxidation catalyst containing molybdenum oxide,tellurium oxide and a vanadium phosphate

ABSTRACT

OXIDATION CATALYSTS USEFUL IN PREPARING UNSATURATED ALDEHYDES AND UNSATURATED CARBOXYLIC ACIDS BY OXIDATION OF UNSATURATED HYDROCARBONS AT AN ELEVATED TEMPERATURE COMPRISE MOLYBDENUM OXIDE, TELLURIUM OXIDE AND A VANADIUM PHOSPHATE.

United States Patent 3,554,928 OXIDATION CATALYST CONTAINING MOLYB-DENUM OXIDE, TELLURIUM OXIDE AND A VANADIUM PHOSPHATE Jamal S. Eden,Akron, Ohio, assignor to The B. F. Goodrich Company, New York, N.Y., acorporation of New York No Drawing. Original application Aug. 30, 1965,Ser. No. 483,866, now Patent No. 3,457,303, dated July 22, 1969. Dividedand this application Jan. 21, 1969, Ser- No. 823,203 The portion of theterm of the patent subsequent to Jan. 11, 1983, has been disclaimed Int.Cl. B01j 11/82 US. Cl. 252-437 4 Claims ABSTRACT OF THE DISCLOSUREOxidation catalysts useful in preparing unsaturated aldehydes andunsaturated carboxylic acids by oxidation of unsaturated hydrocarbons atan elevated temperature comprise molybdenum oxide, tellurium oxide and avanadium phosphate.

This is a division of application Ser. No. 483,866, filed Aug. 30, 1965,now US. Pat. 3,457,303.

This invention relates to new and useful catalysts and to a method ofpreparing unsaturated aldehydes and unsaturated carboxylic acids byoxidation of unsaturated hydrocarbons at an elevated temperature, andrelates more particularly tocatalysts comprising a mixture of amolybdenum oxide, tellurium oxide and a vanadium phosphate in a molarratio of 100 M00 -100 TeO and 10-100 of a vanadium phosphate, and to amethod of preparing acrolein and acrylic acid, or methacrolein andmethacrylic acid by passing vapors of propylene or isobutylene and anoxygen containing gas over the catalyst at a temperature of from about325 C. to about 550 C.

The catalyst can also be designated as lfl 110 220 2-20 39-120 with theP being in the form of a phosphate i.e. each P is attached to 3 or 4oxygen atoms.

Numerous attempts have been made in the past to prepare products ofhigher oxidation state from hydrocarbons, especially from the normallygaseous hydrocarbons. However, all prior catalysts and procedures foroxidizing monoolefinic gaseous hydrocarbons to monoolefinicallyunsaturated aldehydes or monoolefinically unsaturated carboxylic 'acidswith the same number of carbon atoms as the hydrocarbon having seriousshortcomings. The catalysts either have a very short active life, orthey convert only a portion of the hydrocarbon to desired end groups perpass; they oxidize the hydrocarbon excessively to form high proportionsof carbon monoxide or carbon dioxide or both; they are not sufiicientlyselective, so that the hydrocarbon molecule is attacked at both theolefinic unsaturation and at a methyl group; or the oxidation of theolefin does not proceed beyond the aldehyde stage.

It is therefore unexpected to find a catalyst having unusually long lifethat will convert asubstantial amount, more than 50% per pass, of agaseous monoolefin such as propylene or isobutylene to yield very highproportions of acrolein and acrylic acid or methacrolein and methacrylicacid. It is also unexpected to find a catalyst that produces a widerange of ratios of olefinic aldehyde to monoolefinically unsaturatedcarboxylic acid by controllable changes in reaction conditions orcatalyst composition. Mol percent efliciencies of about 10 to 30 for thealdehyde and about 44 for the unsaturated carboxylic acid have beenobtained with the catalyst and process of this invention. This providesa great degree of flexibility in the process, so as to provide means forobtaining a product mix that may be needed at any particular time duringcommercial operation.

THE REACT ANTS The essential reactants are (1) propylene or isobutyleneand (2) an oxygen containing gas, which can be pure oxygen, oxygendiluted with an inert gas, oxygen enriched air or air without additionaloxygen. For reasons of economy, air is the preferred oxygen containingreactant.

For the purpose of this invention the hydrocarbons which are oxidizedcan be defined generally by the formula wherein it is apparent that theend products formed result from the oxidation of only one methyl groupon the hydrocarbon molecule while the terminal remains intact.

Stoichiometric ratios of oxygen to olefin for the purpose of thisinvention are 1.5 to 1. Slightly lower amounts of oxygen can be used ata sacrifice of yield. It is preferred, however, to use 33 to 66% excessoxygen. Larger excesses do not impair the yields of aldehydes and acids,but for practical considerations an excess much above would requireextremely large equipment for a given production capacity.

The addition of steam into the reactor along with the hydrocarbon andoxygen containing gas is desirable but not absolutely essential.Thefunction of steam is not clear, but it seems to reduce the amount ofcarbon monoxide and dioxide in the effluent gases.

Other diluent gases can be used. Surprisingly, saturated hydrocarbonssuch as propane are rather inert under the reaction conditions. Nitrogenor other known inert gases can be used as diluents if desired.

THE CATALYST AND ITS PREPARATION There are several methods for thepreparation of the catalyst, which can be supported or unsupported. Itis possible to dissolve each of the starting ingredients in water andcombine them from the aqueous solutions or the ingredients can be dryblended. Because of the more uniform blend obtained by the solutionprocedure, it is preferred.

A general procedure for preparing a catalyst from water solubleingredients is to dissolve the requisite amount of a molybdenum salt, atellurium salt and a vanadium salt in water. Add the requisite amount ofphosphoric acid to the vanadium salt solution. Add the tellurium saltsolution to the molybdenum salt solution and then add the vanadiumsalt-phosph0ric aicd mixture to the molybdenum-tellurium salt mixture.The catalyst is then dried and baked at 400 C. for about 16 hours.

Supported catalysts can be prepared by adding a dry support or anaqueous slurry thereof to the aqueous solution of catalyst or theaqueous catalyst ingredients can be added to the slurry of the support.

Alternatively a slurry of the catalyst ingredients can be prepared inwater, then dried and baked. For supported catalysts the aqueous slurryof the catalyst ingredients can be added to an aqueous suspension of thesupport or vice versa, and then dried and baked.

Another method is to blend the dry ingredients of the desired particlesize and then mix them thoroughly. Thorough blending and uniformparticle size is desired.

A specific example of the solution method is now set forth. Thereactants are:

(1) 86.38 g. molybdic acid (99% (2) 31.922 g. TeO dissolved in 80 ml. ofconcentrated HCl.

(3) 22.06 g. of VOC1 dissolved in 1:1 nitric acid water.

(4) 18.48 g. of H PO (85% 1) is added to 200 grams of an aqueouscolloidal dispersion of microspheroidal silica in a concentration of30-35% SiO (Ludox H.S.), then (2), then (3) and (4). Dry the mixture ona steam bath and bake for 16 hours at 400 C. Thereafter, the catalyst isground to the desired mesh size and sieved.

The silica may also be added to one of the individual ingredients. Amongthe suitable supports are silica, silica containing materials, such asdiatomaceous earth, kieselguhr, silicon carbide, clay, aluminum oxidesand even carbon, although the latter tends to be consumed during thereaction.

The exact chemical structure of the catalysts made by the aboveprocedures is not known, but catalysts with molar ratios of 100 Mo,10-100 Te and 10100 of a vanadium phosphate can be used for oxidizingthe monoolefinic hydrocarbon to aldehyde and/or carboxylic acid. Thecatalyst contains chemically bound oxygen so that the generic formulacan be written as a-100 2-1o 10o( )2 2 .7

or other vanadyl phosphate REACTION CONDITIONS The reaction can becarried out in either a fixed or fluidized catalyst bed.

The reaction temperature can range from about 300 to 450 C. for theoxidation of propylene but the preferred range is from about 325 toabout 400 C. Below 325 C. the conversion per pass is lower and lowtemperature tends to produce more aldehyde than desired. Usually, alonger contact time is needed at lower temperatures to obtain the yieldsof desired products obtainable at higher temperatures. Above 425 C. inthe propylene oxidation some of the desired end products appear to beoxidized to carbon oxides. This is much more apparent at 450 C. Forisobutylene, oxidation temperatures of 375-550 are desirable with thepreferred range being 300450 C.

The molar ratio of oxygen to propylene or isobutylene should be at least2 to l for good conversion and yields. Some excess oxygen, 33 to 66 molpercent is even more desirable and is preferred. There is no criticalupper limit as to the amount of oxygen, but when air is used as theoxygen containing gas it becomes apparent that too great an excess willrequire large reactors, pumping, compressing and other auxiliaryequipment for any given amount of desired end product. It is thereforebest to limit the amount of air to provide a 33 to 66% excess of oxygen.This range provides the largest proportion of acid, under given reactionconditions. Also, since care is needed to avoid an explosive mixture,the limiting of air aids in that direction.

The molar ratio of steam to propylene or isobutylene can range from 0 toabout 5 to 7, but best results are obtained with molar ratios of about 3to 5 per mol of olefin and for this reason are preferred.

The contact time can vary considerably in the range of about 2 to 70seconds. Best results are obtained in a range of about 8 to 54 secondsand this range is preferred. Longer contact times usually favor theproduction of acid at any given temperature.

The particle size of catalyst for fixed bed operations used is from10-18 mesh. As is known, for fixed beds, the size may be of a Widerrange particle size. For fluid 4 bed systems the catalyst size should befrom 325 mesh (U.S. Sieve).

The reaction can be run at atmospheric pressure, in a partial vacuum orunder induced pressure up to 50100 p.s.i. Atmospheric pressure ispreferred for fixed bed systems and a pressure of 1 to 100 p.s.i. forfluid bed reactions. Operation at a pressure which is below the dewpoint of the unsaturated acid at the reaction temperature isadvantageous.

Wide variations in percentages of unsaturated acids and aldehydes can beobtained with a single catalyst, using fixed ratio of reactants butchanging the temperatures and/or contact time. Further variation isobtainable by controlling the other variables in the reaction includingthe catalyst compositions within the limits set forth herein.

The examples are intended to illustrate the invention but not to limitit.

THE EXAMPLES A series of runs was made in a fixed bed reactor of a highsilica (Vycor) glass tube 12 inches long and 30 mm. outer diameter. Thereactor had three inlets, one for air, one for steam and one forpropylene. Three external electrically operated heating coils were woundon the reactor. One of the coils extended along the entire length of thereactor and each of the remaining coils extended only about one half thelength of the reactor.

Outlet vapors were passed through a short water cooled condenser.Uncondensed gasses were passed through a gas chromatograph (Perkin-Elmermodel 154D) and analyzed continuously. The liquid condensate was weighedand then analyzed for acrylic acid and acrolein in the gaschromatograph.

The reactor was filled to about of its capacity with 170 ml. of acatalyst made by the solution method described above, using a ratio of75 M00 25 TeO and 12.5 (VO) P O Empirically the catalyst is and the P ispresent as P 0 Steam at a temperature of 200-250 C. was first passedinto the reactor. Then propylene and air were separately fed into thestream of water vapor. This mixture then passed through a pre-heater andentered the reactor at about 200-250 C, The reactor was pre-heated toabout 285 C. before the gas feed was begun.

The ratio of reactants was about 2.955 mols of oxygen per mol ofpropylene. The steam and cold contact time are set forth in the tablebelow. The reaction temperature was varied as the reaction proceeded.

The table below summarizes the data obtained in these runs:

M01 percent yield on M01 propylene Contact percent converted Steam,Temp., time, propylene mols 0. seconds converted Aer. AA.

No'rE.Acr.=Acrolcin; AA=Acrylic acid. The mol percent efficiency is thesame as the yield since 100% conversion was obtained.

phate in a molar ratio of 100 molybdenum oxide, 1010O tellurium oxideand 10-100 of vanadium phosphate.

2. A composition of claim 1 wherein the vanadium phosphate is vanadylpyrophosphate.

3. The composition of claim 2 having a molar ratio of about 75 M00 25TeO and 12.5 (VO)2P2O7.

4. The composition of claim 1 on a silicic support.

6 Minekawa et al, 260-604X Eden 252-437 Koch 260604X Eden 252437 PATRICKP. GARVIN, Primary Examiner US. Cl. X.R.

(5/59) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,554,928 Dated January 12, 1971 Inventor-(:6 J3me; 5, Eden It iscertified that error a ppears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2, line 15, "generally" should read --generica1ly--; line 20,"6-011 should read --C=CH line 25,

"GH -Eh" should read CH =EJ- Signed and sealed this 1st day of June1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SGHUYLER, JR Attesting OfficerCommissioner of Patents

